Systems and methods for UE positioning in a distributed antenna wireless system

ABSTRACT

In some embodiments, a node associated with a distributed antenna wireless system obtains one or more combined receive signals responsive to a transmission by the wireless device. The distributed antenna wireless system comprises multiple Remote Radio Heads (RRHs) each comprising one or more receivers. Each receive branch of one or more receive branches of the distributed antenna wireless system comprises a combination of one receiver from each of the RRHs. The one or more combined receive signals comprise, for each receive branch, a combined receive signal that is a combination of signals received by the receivers comprised in the receive branch in accordance with different simultaneous ON/OFF patterns assigned to the RRHs for the receive branches. The node analyzes the one or more combined receive signals to determine information indicative of a geographic location of the wireless device.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/782,979, filed Oct. 7, 2015, now U.S. Pat. No. 9,906,911, which is a35 U.S.C. § 371 national phase filing of International Application No.PCT/IB2015/056777, filed Sep. 4, 2015, the disclosures of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to wireless device positioning in adistributed antenna wireless system.

BACKGROUND

When deploying wireless communications networks, there is a balancebetween coverage and capacity. On the one hand, a deployment including afew large cells can provide great coverage but at a cost of reducedcapacity. On the other hand, a deployment with many small cells createsbetter capacity and throughput, but may not provide the desiredcoverage. Hence, there is often a combination of larger cells to providesufficient coverage with smaller cells to provide better capacity.However, when the cells get too small, wireless terminals moving in thenetwork cause a great number of handovers which causes significantoverhead. Moreover, providing coverage indoors using many small cellscan be quite costly, with a radio base station for each such small cell.

One solution to these problems is to use Remote Radio Heads (RRHs),where several RRHs connected to the same radio base station share thesame cell. In this way, a single radio base station can, e.g., providecoverage in different parts of an indoor environment (e.g., a building)by placing the RRHs appropriately. Moreover, a wireless device can movebetween the coverage of different RRHs while staying within the samecell, thereby avoiding handovers.

Against this backdrop, User Equipment (UE) is a core requirement inEnhanced-911 (E911) and other services provided in a wireless network.Standard and regulatory bodies such as the Third Generation PartnershipProject (3GPP) and the Federal Communications Commission (FCC) haveincreased their location requirements on the precision of indoor UElocation.

However, since a single cell is spanned by multiple RRHs, thegranularity of location determination is quite large. This leads toinsufficient positioning accuracy in locating wireless devices, leadingto issues in complying with increased accuracy of positioningrequirements for emergency calls such as those specified in E911 by theFCC Communications Security, Reliability, and Interoperability Council(CSRIC). Positioning is also beneficial for other types of services,such as for targeted location based messaging. Since the RRHs are oftendeployed indoors, satellite based positioning such as Global PositioningSystem (GPS) is often unavailable.

As such, there is a need for systems and methods for determining thelocation of wireless devices (e.g., UEs) in a distributed antenna system(e.g., a cellular network deployment utilizing multiple RRHs in a singlecell, e.g., in an indoor environment).

SUMMARY

Systems and methods relating to locating a wireless device in adistributed antenna wireless system are disclosed. In some embodiments,a node associated with a distributed antenna wireless system is operableto determine a geographic location of a wireless device. The nodeobtains one or more combined receive signals responsive to atransmission by the wireless device. The distributed antenna wirelesssystem comprises multiple Remote Radio Heads (RRHs) each comprising oneor more receivers. Each receive branch of one or more receive branchesof the distributed antenna wireless system comprises a combination ofone receiver from each of the RRHs. The one or more combined receivesignals comprise, for each receive branch of the distributed antennawireless system, a combined receive signal that is a combination ofsignals received by the receivers comprised in the receive branch inaccordance with different simultaneous ON/OFF patterns assigned to theRRHs for the one or more receive branches. The node analyzes the one ormore combined receive signals to determine information indicative of ageographic location of the wireless device.

In some embodiments, each RRH comprises multiple receivers, the one ormore receive branches is multiple receive branches wherein each receivebranch comprises a combination of one of the receivers from each of theRRHs, and the one or more combined receive signals is multiple combinedreceive signals that comprise, for each receive branch, a combinedreceive signal that is a combination of signals received by thereceivers comprised in the receive branch in accordance with differentsimultaneous ON/OFF patterns assigned to the RRHs for the receivebranches.

In some embodiments, the node is further operable to assign thedifferent simultaneous ON/OFF patterns to the RRHs for the receivebranches. In some embodiments, the node randomly assigns the differentsimultaneous ON/OFF patterns to the RRHs for the receive branches.

In some embodiments, the node is further operable to configure the RRHswith the different simultaneous ON/OFF patterns assigned to the RRHs forthe receive branches. In other embodiments, the signals received by thereceivers are combined by an Intermediate Radio Unit (IRU), and the nodeis further operable to configure the IRU with the different simultaneousON/OFF patterns assigned to the RRHs for the receive branches.

In some embodiments, the node is further operable to trigger thetransmission by the wireless device. In some embodiments, the node isfurther operable to trigger the transmission by the wireless device viaa paging message such that the transmission is a page response. In otherembodiments, the node is further operable to trigger the transmission bythe wireless device via an uplink grant such that the transmission is anuplink data transmission in accordance with the uplink grant.

In some embodiments, in order to analyze the combined signals, the nodeis further operable to obtain measurements of received signal energyand/or characteristic(s) for the combined signals within a predefinedfrequency range used for the transmission by the wireless device duringa corresponding time window, and compare the measurements for thecombined receive signals to the different simultaneous ON/OFF patternsassigned to the RRHs for the receive branches of the distributed antennawireless system to identify one of the RRHs that is closest to thewireless device as a closest RRH.

Further, in some embodiments, the node is further operable to change thedifferent simultaneous ON/OFF patterns assigned to the RRHs; and, afterchanging the different simultaneous ON/OFF patterns assigned to theRRHs, repeat the process of obtaining combined receive signalsresponsive to a transmission by a wireless device and analyzing thecombined receive signals to determine information indicative of thegeographic location of the wireless device.

In some embodiments, the node is further operable to assign andconfigure a different ON/OFF pattern for the closest RRU and each RRU ofmultiple neighboring RRUs of the closest RRU, trigger a secondtransmission by the wireless device, and triangulate the geographiclocation of the wireless device based on second combined signalsobtained for the receive branches of the distributed antenna wirelesssystem responsive to the second transmission by the wireless device.

In some embodiments, the node is further operable to use the informationindicative of the geographic location of the wireless device toselectively activate transmitters and/or receivers of one or more of theRRHs for communication with the wireless device.

In other embodiments, a node associated with a distributed antennawireless system is operable to determine a geographic location of awireless device. The node is operable to divide RRHs in the distributedantenna wireless system into M zones, where M is equal to a selectnumber of different simultaneous ON/OFF patterns for receive branches ofthe distributed antenna wireless system. The node is further operable toassign and configure a different simultaneous ON/OFF pattern for theplurality of receive branches to each of the M zones, trigger atransmission by a wireless device, and analyze resulting combinedreceive signals for the receive branches to identify a zone, from the Mzones, in which the wireless device is located. The node is furtheroperable to, if the number of RRHs in the identified zone is less thanor equal to a threshold, the threshold being equal to or less than anumber of available different simultaneous ON/OFF patterns, assign andconfigure a different simultaneous ON/OFF pattern for the receivebranches to each of the RRHs in the identified zone, trigger atransmission by the wireless device, and analyze resulting combinedreceive signals for the receive branches to identify the RRH, from theRRHs in the identified zone, that is closest to the wireless device.

In some embodiments, the node is further operable to, if the number ofRRHs in the identified zone is greater than the threshold, divide theRRHs in the identified zone into J subzones, where J is equal to aselect number of different simultaneous ON/OFF patterns for the receivebranches of the distributed antenna wireless system and J may or may notbe equal to M. The node is further operable to assign and configure adifferent simultaneous ON/OFF pattern for the receive branches to eachof the J subzones, trigger a transmission by the wireless device, andanalyze resulting combined receive signals for the receive branches toidentify a subzone, from the J subzones, in which the wireless device islocated.

Further, in some embodiments, the node is further operable tosuccessively repeat the steps of dividing the identified (sub)zone intoJ subzones, assigning and configuring a different simultaneous ON/OFFpattern for the receive branches to each of the J subzones, triggering atransmission by the wireless device, and analyzing resulting combinedreceive signals for the receive branches to identify a subzone in whichthe wireless device is located until the number of RRHs in theidentified subzone is less than or equal to the threshold.

In some embodiments, the node is further operable to, when the number ofRRHs in the identified subzone is less than or equal to the threshold,assign and configure a different simultaneous ON/OFF pattern for thereceive branches to each of the RRHs in the identified subzone, triggera transmission by the wireless device, and analyze resulting combinedreceive signals for the receive branches to identify the RRH, from theRRHs in the identified subzone, that is closest to the wireless device.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the embodiments in association withthe accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIGS. 1A and 1B illustrate a distributed antenna wireless systemaccording to some embodiments of the present disclosure;

FIG. 2 is a more detailed block diagram of a Remote Radio Head (RRH)according to some embodiments of the present disclosure;

FIGS. 3A and 3B illustrate one example of assigning simultaneousreceiver ON/OFF patterns to the RRHs in a distributed antenna wirelesssystem;

FIG. 4 illustrates the use of Fast Fourier Transform (FFT) outputs assignal strength measurements for the appropriate frequency and timeresources used for uplink transmission by a wireless device andcomparison of the signal strength measurements to the assigned ON/OFFpatterns to determine the RRH closest to the wireless device accordingto some embodiments of the present disclosure;

FIG. 5 illustrates a process for determining the location of a wirelessdevice in a distributed antenna wireless system according to someembodiments of the present disclosure;

FIG. 6 is a flow chart that illustrates a process improving theprecision of the location estimate for the wireless device according tosome embodiments of the present disclosure;

FIGS. 7A and 7B illustrate a process for determining the location of awireless device in a distributed antenna wireless system according tosome other embodiments of the present disclosure; and

FIG. 8 graphically illustrates one example of the use of the determinedlocation of a wireless device according to some embodiments of thepresent disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent information to enable thoseskilled in the art to practice the embodiments and illustrate the bestmode of practicing the embodiments. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the disclosure and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

Systems and methods for wireless device positioning in a distributedantenna wireless system are disclosed. In this regard, FIG. 1Aillustrates a distributed antenna wireless system 10 according to someexample embodiments of the present disclosure. In particular, thedistributed antenna wireless system 10 is, in some preferredembodiments, a base station and associated Remote Radio Heads (RRHs)serving a cell in a cellular communications network. As illustrated, inthis example, the distributed antenna wireless system 10 includes abaseband unit 12, an Intermediate Radio Unit (IRU) 14 (which issometimes referred to as an Indoor Radio Unit), and a number (N) of RRHs16-1 through 16-N (which are generally referred to herein collectivelyas RRHs 16 and individually as RRH 16), where N is greater than 1 and,in many deployment scenarios, is much greater than 1. For example, insome embodiments, the baseband unit 12 is implemented in a base station(e.g., a Third Generation Partnership Project (3GPP) Long Term Evolution(LTE) enhanced or evolved Node B (eNB)). Note that while in this examplethere is one baseband unit 12, one IRU 14, and multiple RRHs 16, thepresent disclosure is not limited thereto. In some other embodiments,there may be multiple IRUs 14 and multiple RRHs 16. Further, whileseparate in the illustrated example, in some other embodiments, thebaseband unit 12 and the IRU 14 may be implemented together as a singleunit.

The systems and methods disclosed herein are particularly beneficial indeployments where the RRHs 16 are in an indoor environment such as,e.g., inside a building, but are not limited thereto. The RRHs 16 aregenerally radios (e.g., Radio Frequency (RF) front-ends) distributedthroughout an environment and are, therefore, remote from the basebandunit 12 and the IRU 14. Note that the implementation of the RRHs 16illustrated in FIG. 1A and described herein is only an example. The RRHs16 can have different configurations depending on the particularimplementation. For example, in some embodiments, the RRHs 16 includeonly the RF front end. However, in other embodiments, the RRHs 16 alsoinclude the IRU 14 (i.e., an intermediate frequency processing unit). Inother words, in some other embodiments, the functionality of the IRU 14may be distributed among the RRHs 16.

The RRHs 16 include, among other things, receivers (RXs) 18 coupled tocorresponding antennas 20. In this particular example, the distributedantenna wireless system 10 is a 4×4 Multiple Input Multiple Output(MIMO) system that includes four receive branches, which are referred toherein as receive branches A, B, C, and D. As such, in this example, theRRH 16-1 includes receiver 18-1A that is coupled to antenna 20-1A forreceive branch A, receiver 18-1B that is coupled to antenna 20-1B forreceive branch B, receiver 18-1C that is coupled to antenna 20-1C forreceive branch C, and receiver 18-1D that is coupled to antenna 20-1Dfor receive branch D. Likewise, the RRH 16-2 includes receiver 18-2Athat is coupled to antenna 20-2A for receive branch A, receiver 18-2Bthat is coupled to antenna 20-2B for receive branch B, receiver 18-2Cthat is coupled to antenna 20-2C for receive branch C, and receiver18-2D that is coupled to antenna 20-2D for receive branch D; and the RRH16-N includes receiver 18-NA that is coupled to antenna 20-NA forreceive branch A, receiver 18-NB that is coupled to antenna 20-NB forreceive branch B, receiver 18-NC that is coupled to antenna 20-NC forreceive branch C, and receiver 18-ND that is coupled to antenna 20-NDfor receive branch D. Note that 4×4 MIMO is only an example. Thedistributed antenna wireless system 10 may include any number of one ormore receive branches, where the RRHs 16 may include any number of oneor more receivers 18. Further, different RRHs 16 may include differentnumbers for the same number of receivers 18, depending on the particularimplementation.

As discussed below, signals received by the receivers 18-1A, 18-2A, . .. , 18-NA of the RRHs 16-1, 16-2, . . . , 16-N, respectively, arecombined in the IRU 14 to provide a combined signal for receive branchA. Likewise, the signals received by the receivers 18-1B, 18-2B, . . . ,18-NB of the RRHs 18-1, 18-2, . . . , 18-N, respectively, are combinedin the IRU 14 to provide a combined signal for receive branch B; thesignals received by the receivers 18-1C, 18-2C, . . . , 18-NC of theRRHs 18-1, 18-2, . . . , 18-N, respectively, are combined in the IRU 14to provide a combined signal for receive branch C; and the signalsreceived by the receivers 18-1D, 18-2D, . . . , 18-ND of the RRHs 18-1,18-2, . . . , 18-N, respectively, are combined in the IRU 14 to providea combined signal for receive branch D. This is illustrated in FIG. 1B.

Satisfying UE location requirements for UEs served by the distributedantenna wireless system 10, particularly in an indoor environment, ischallenging. Specifically, when using macro base stations in an outdoorenvironment, triangulation may be used to further pinpoint the locationof a UE within a cell. However, in the distributed antenna wirelesssystem 10 the RRHs 16 are typically homogeneous (i.e., the same). Theuplink signals received by the various receivers 18 of the RRHs 16 arecombined to provide the combined receive signals for the correspondingreceive branches of the distributed antenna wireless system 10. Inconventional systems, when a particular UE transmits an uplink signal,the baseband unit 12 cannot then determine which of the RRHs 16 receivedthe uplink signal (or at least which RRH 16 received the uplink signalwith the strongest signal strength). As such, the baseband unit 12 is,in conventional systems, unable to determine which RRH 16 is closest tothe UE and is also unable to triangulate the location of the UE withinthe cell served by the RRHs 16.

In order to overcome these challenges, the distributed antenna wirelesssystem 10 utilizes different simultaneous ON/OFF patterns for thereceive branches for the RRHs 16 to enable the baseband unit 12 to,e.g., determine the RRH 16 that is closest to a particular UE. As usedherein, an ON/OFF pattern assigned to a RRH 16 is a unique pattern thatdefines an ON/OFF state of the receivers 18 of that RRH 16 during a timewindow in which a transmission of a UE (for which the location is to bedetermined) is received. As used herein, the ON state of a receiver 18can be controlled at the receiver 18 or the corresponding RRH 16 by,e.g., disabling the receiver 18 or can be controlled at the IRU 14 by,e.g., controlling a gain applied to the received signal from thereceiver 18 (e.g., applying a gain of 1 for the ON state or applying again of zero for the OFF state). Thus, the ON state is to be understoodas the equivalent to setting the gain for the received signal from thereceiver 18 to 1 or sufficiently high so that the amount of energyreceived is interpreted as a signal being received. Conversely, as usedherein, the OFF state of a receiver 18 can be controlled at the receiver18 or the corresponding RRH 16 by, e.g., enabling the receiver 18 or canbe controlled at the IRU 14 by, e.g., controlling a gain applied to thereceived signal from the receiver 18. Thus, the OFF state is to beunderstood as the equivalent to setting the gain for the received signalfrom the receiver 18 to zero or sufficiently low so that the amount ofenergy received is interpreted as no signal being received.

By assigning different simultaneous ON/OFF patterns to different RRHs16, the baseband unit 12 is then able to analyze the combined signalsfor the received branches to determine which of the RRHs 16 is closestto the UE. Since the RRHs 16 are typically arranged in a densedeployment (e.g., 20 meter (m) or less spacing between the RRHs 16,according to one exemplary embodiment), the location of the UE is thenknown to within a predetermined precision range (e.g., ±10 m in adeployment that uses 20 m spacing between the RRHs 16). In someembodiments, additional procedures may be performed to further improvethe precision of the determined location of the UE.

In this regard, the baseband unit 12 includes an ON/OFF patternassignment generator 22, a UE location calculator 24, a Fast FourierTransform (FFT) bank 26, and baseband processing circuity 28, each ofwhich is implemented in hardware or a combination of hardware andsoftware (e.g., software stored in memory and executed by one or moreprocessors). Notably, while the ON/OFF pattern assignment generator 22and the UE location calculator 24 are illustrated as being implementedin the baseband unit 12 in embodiments described herein, thefunctionality of the ON/OFF pattern assignment generator 22 and/or theUE location calculator 24 may be implemented in another node(s) in orassociated with the distributed antenna wireless system 10 and/ordistributed among multiple nodes (e.g., the baseband unit 12 and othernode(s)).

As discussed below, the ON/OFF pattern assignment generator 22 operatesto assign simultaneous ON/OFF patterns to the RRHs 16 and configure theRRHs 16 and/or the IRU 14 with the assigned ON/OFF patterns. Notably, insome embodiments, the number of unique ON/OFF patterns available forassignment is greater than or equal to the number (N) of RRHs 16 and, assuch, each of the RRHs 16 is assigned a different ON/OFF pattern.However, in other embodiments, the number of unique ON/OFF patternsavailable for assignment is less than the number (N) of RRHs 16 and thepatterns are assigned to different RRH zones (i.e., different sets ofthe RRHs 16). A search procedure may then be performed to determine theRRH 16 that is closest to the UE of interest. The UE location calculator24 operates to calculate, or otherwise determine, the location of a UEof interest based on a comparison of outputs of the FFT bank 26 for eachof the combined receive signals and the ON/OFF patterns assigned to theRRHs 16. Notably, while the FFT bank 26 is used in the embodimentsdescribed herein, the present disclosure is not limited to the use ofthe FFT bank 26. Other mechanisms for measuring the received signalstrength and/or characteristic of the combined signals in theappropriate frequency range and time window (corresponding to an uplinktransmission from a UE to be located) can be used. For example, bandpassfilters and power meters may alternatively be used. The basebandprocessing circuitry 28 performs normal or conventional basebandprocessing of the FFT transformed combined receive signals for thereceive branches of the distributed antenna wireless system 10.

The IRU 14 includes an RRH interface 30, receive circuitry 32-A through32-D for the receive branches, transmit circuitry 34-A through 34-D fortransmit branches, and a radio controller 36, each of which isimplemented in hardware or a combination of hardware and software. TheRRH interface 30 generally operates to combine signals received by thereceivers 18-1A, 18-2A, . . . , 18-NA of the RRHs 16-1, 16-2, . . . ,16-N, respectively, to provide a combined signal for receive branch A,which is then processed by the receive circuitry 32-A for receive branchA. Likewise, the RRH interface 30 combines signals received by thereceivers 18-1B, 18-2B, . . . , 18-NB of the RRHs 16-1, 16-2, . . . ,16-N, respectively, to provide a combined signal for receive branch B,which is then processed by the receive circuitry 32-B for receive branchB. The RRH interface 30 combines signals received by the receivers18-1C, 18-2C, . . . , 18-NC of the RRHs 16-1, 16-2, . . . , 16-N,respectively, to provide a combined signal for receive branch C, whichis then processed by the receive circuitry 32-C for receive branch C.The RRH interface 30 combines signals received by the receivers 18-1D,18-2D, . . . , 18-ND of the RRHs 16-1, 16-2, . . . , 16-N, respectively,to provide a combined signal for receive branch D, which is thenprocessed by the receive circuitry 32-D for receive branch D. Thereceive circuitry 32 may perform any suitable receive operations suchas, for example, filtering, Analog to Digital (A/D) conversion, or thelike. In this example, the combined receive signals output by thereceive circuitry 32 are provided to the baseband unit 12 via the radiocontroller 36.

In a similar manner, with respect to transmission, a transmit signal isprovided to the IRU 14 from the baseband unit 12. The transmit signal isprovided to the transmit circuitry 34-A through 34-D for the transmitbranches A through D, respectively. The transmit circuitry 34 performsany suitable transmit processing such as, for example, Digital to Analog(D/A) conversion, filtering, or the like. The resulting transmit signalsare provided to the RRH interface 30, where the transmit signals aresplit and provided to the RRHs 16 for transmission.

FIG. 2 illustrates the RRH 16 in more detail according to someembodiments of the present disclosure. Note that the RRH 16 of FIG. 2 isany one of the RRHs 16-1, 16-2, 16-3, and 16-4 of FIGS. 1A and 1B. Inother words, FIG. 2 and the following discussion is equally applicableto each of the RRHs 16-1, 16-2, 16-3, and 16-4 of FIGS. 1A and 1B. Assuch, in this context, the receivers 18 of the RRH 16 of FIG. 2 arereferred to as receivers 18-A, 18-B, 18-C, and 18-D.

As illustrated, the RRH 16 includes Input/Output (I/O) circuits 38-Athrough 38-D. The receivers 18-A through 18-D include duplexers 40-Athrough 40-D, amplifiers 42-A through 42-D, and down-conversion andfiltering circuitry 44A through 44D, respectively. The RRH 16 alsoincludes transmitters formed by up-conversion and filtering circuitry46-A through 46-D, amplifiers 48-A through 48-D, and the duplexers 40-Athrough 40-D, respectively. The RRH 16 also includes a control system 50that, at least in some embodiments, operates to activate/deactivate thereceivers 18 of the RRH 16 according to the ON/OFF pattern with which itis configured. In this example, the control system 50 activates (i.e.,turns “ON”) and deactivates (i.e., turns “OFF”) the receivers 18 by,e.g., controlling the corresponding amplifiers 42 (e.g., turn off theamplifier 42 to turn off the corresponding receiver 18) and/orcontrolling the corresponding down-conversion and filtering circuitry 44(e.g., opening a switch within the down-conversion and filteringcircuitry 44 to turn off the corresponding receiver 18). However, otheractivation/deactivation mechanisms can be used.

FIGS. 3A and 3B illustrate the assignment of different simultaneousON/OFF patterns to the RRHs 16 according to one example embodiment ofthe present disclosure. In this example, as illustrated in FIG. 3A,there are sixteen RRHs 16, referenced as RRH 1 through RRH 16. Thedistributed antenna wireless system 10 has four receive branches,namely, receive branches A, B, C, and D; and each of the RRHs 16 hasfour receivers 18 for the four receive branches, respectively. Asillustrated in FIG. 3B, the RRHs 16 are assigned different simultaneousON/OFF patterns.

As an example, RRH 12 is assigned the ON/OFF pattern of 1011 (i.e., ON,OFF, ON, ON) such that the receiver 18-A of RRH 12 for receive branch Ais ON, the receiver 18-B of RRH 12 for receive branch B is OFF, thereceiver 18-C of RRH 12 for receive branch C is ON, and the receiver18-D of RRH 12 for receive branch D is ON. Therefore, as discussedbelow, when determining the location of a UE, this ON/OFF pattern isapplied during reception of an uplink transmission from that UE. If theUE happens to be in the coverage area of the RRH 12, the uplinktransmission will appear sufficiently strong in branches A, C, and D tobe considered ON, but will appear sufficiently diminished in branch B tobe considered OFF or ‘mute’ or ‘silent’. This pattern is detected by thebaseband unit 12, and in particular detected by the UE locationcalculator 24 by analyzing the outputs of the FFT bank 26 for thecombined receive signals for the four receive branches. This isillustrated in FIG. 4 where the outputs of FFTs 52A, 52-B, and 52-D forbranches A, C, and D, respectively, have large magnitudes in thefrequency bin that corresponds to the known frequency resources (e.g.,subcarrier frequencies) used for the uplink transmission, whereas theoutput of FFT 52-B for branch B has a small magnitude (e.g., due to asmall signal strength received at some neighboring RRHs 16) in thefrequency bin that corresponds to the known frequency resources used forthe uplink transmission. Once the pattern is detected, the UE locationcalculator 24 can determine, based on a comparison of the detectedpattern and the known patterns assigned to the RRHs 16, that thedetected pattern is the pattern assigned to RRH 12. As a result, the UElocation calculator 24 knows that the RRH 12 is the closest RRH to theUE. In this manner, the location of the UE is determined. For instance,if the RRHs 16 are spaced 20 m apart, the UE location calculator 24knows that the UE is located ±10 m from the known location of RRH 12.Note that, as discussed below, further procedures may be performed insome embodiments to further improve the precision of the locationestimate for the UE.

FIG. 5 illustrates the operation of the distributed antenna wirelesssystem 10 to determine the location of a UE 54 (which may more generallybe referred to herein as a wireless device) according to someembodiments of the present disclosure. As illustrated, the baseband unit12, and in particular the ON/OFF pattern assignment generator 22,assigns different unique ON/OFF patterns to the RRHs 16 for thereceivers 18 of the receive branches of the distributed antenna wirelesssystem 10 (step 100). The ON/OFF patterns are also referred to herein assimultaneous ON/OFF patterns to emphasize that the ON/OFF patternsdefine the simultaneous ON/OFF states of the receivers 18 of the RRHs16. In this embodiment, each of the RRHs 16 is assigned a differentON/OFF pattern. In other words, the number of available ON/OFF patternsis greater than or equal to the number of RRHs 16. The ON/OFF patternsmay be assigned using any suitable assignment scheme such as, forexample, randomly or is some predefined manner. For example, in someembodiments, Grey codes may be used when assigning the ON/OFF patterns.

The baseband unit 12, and in particular the ON/OFF pattern assignmentgenerator 22, then configures the IRU 14 and/or the RRHs 16 with theassigned ON/OFF patterns (step 102). In some embodiments, the basebandunit 12 configures the RRHs 16 with the assigned ON/OFF patterns, inwhich case the RRHs 16 activate/deactivate their receivers 18 accordingto the configured ON/OFF patterns. This configuration of the RRHs 16may, in some embodiments, be made by the IRU 14 under the control of thebaseband unit 12 (e.g., the baseband unit 12 may provide the assignedON/OFF patterns to the IRU 14, where the IRU 14 then controls/configuresthe RRHs 16 according to the assigned ON/OFF patterns). However, inother embodiments, the baseband unit 12 may alternatively configure theIRU 14 with the ON/OFF patterns for the RRHs 16 such that the IRU 14combines the signals from the receivers 18 of the RRHs 16 for thedifferent receive branches according to the ON/OFF patterns assigned andconfigured for the RRHs 16. For example, the IRU 14 may mute the signalsfrom the receivers 18 that are configured as OFF (e.g., using switchesor amplifying with a gain of zero) such that the combined signals arethe combination of only those signals received by the receivers 18 thatare configured as ON. In this manner, the IRU 14 effectively turns thereceivers 18 of the RRHs 16 ON/OFF according to the assigned andconfigured ON/OFF patterns.

In some embodiments, the baseband unit 12, and in particular the UElocation calculator 24, triggers an uplink transmission by the UE 54(step 104). As indicated by the dashed line, this is an optional stepthat may not be performed in all embodiments. In some embodiments, theuplink transmission is triggered by paging the UE 54 by transmitting theappropriate paging message via the IRU 14 and the RRHs 16. This isparticularly beneficial if the UE 54 is in IDLE state. In otherembodiments, the uplink transmission is triggered by transmitting anuplink grant to the UE 54 via the IRU 14 and the RRHs 16. This isparticularly beneficial if the UE 54 is in the CONNECTED or ATTACHEDstate. In either case, the baseband unit 12 knows which time andfrequency resources will be used by the UE 54 for the triggered uplinktransmission. As such, the configuration in step 102 is for theappropriate time window during which the triggered uplink transmissionwill occur.

The UE 54 then transmits an uplink transmission (e.g., a page responseor an uplink data transmission) (step 106). The RRHs 16, and inparticular the receivers 18 of the RRHs 16, listen for the uplinktransmission and send resulting uplink, or received, signals to the IRU14 (step 108). In some embodiments where the ON/OFF patterns areconfigured at the RRHs 16, the receivers 18 of the RRHs 16 are ON/OFFaccording to the configured ON/OFF patterns during reception of theuplink transmission. The IRU 14 combines the received signals to providecombined receive signals for the different receive branches (e.g.,receive branches A, B, C, and D) of the distributed antenna wirelesssystem 10 (step 110). In some embodiments where the ON/OFF patterns areconfigured at the IRU 14, the IRU 14 combines the received signalsaccording to the ON/OFF patterns assigned to the corresponding RRHs 16.

The IRU 14 provides the combined signals to the baseband unit 12 (step112). At this point, whether the ON/OFF patterns are applied at the IRU14 or the RRHs 16, the combined signals are provided according to theassigned and configured ON/OFF patterns. The baseband unit 12, and inparticular the UE location calculator 24, analyzes the combined signals(and, in particular, the results of FFTs of the combined signals) todetermine, e.g., the location of the UE 54 (step 114). Morespecifically, the baseband unit 12 performs an FFT of each of thecombined signals. The characteristic and/or magnitude of the FFTs forthe frequency bin(s) corresponding to the frequency resource(s) on whichthe uplink transmission was transmitted are analyzed to determine anobserved ON/OFF pattern. The observed ON/OFF pattern is then compared tothe known, assigned ON/OFF patterns for the RRHs 16 to thereby determinethe assigned pattern that matches the observed pattern. The RRH 16 towhich the observed pattern was assigned is determined to be the closestRRH 16 to the UE 54 and, as such, the location of the UE 54 isdetermined to be within some predefined range (e.g., ±10 m if the RRHs16 are installed 20 m apart from one another) from the closet RRH 16.This predefined range depends on the known spacing between the RRHs 16.As such, the precision of the determined location of the UE 54 in step114 depends on the spacing, or density, of the RRHs 16. For example, ifthe spacing of the RRHs 16 is reduced to 10 m, then the precision of thelocation determined in step 114 can be improved to ±5 m.

Optionally, the baseband unit 12, and in particular the ON/OFF patternassignment generator 22, changes the ON/OFF pattern assignments (e.g.,randomly) and the process (i.e., steps 102-114) is repeated using thenew assignments (step 116). This may be repeated one or more times. Thelocation of the UE 54 may then be determined based on the results of themultiple iterations of the process (step 118). More specifically, eachof the multiple, or successive, iterations produces a result. If allresults are the same, the confidence level for the determined locationincreases. Repeating the process with new ON/OFF pattern assignments maybe beneficial because, e.g., the receivers 18 of the RRHs 16 may haveslightly different receiver sensitivity due to, e.g., manufacturingtolerances. Repeating the process with changing ON/OFF patternassignments helps to improve the accuracy of the UE locationdetermination.

In some implementations, it may be desirable to achieve greaterprecision in the location determined for the UE 54. In this regard, FIG.6 illustrates a process by which a more precise location of the UE 54can be determined according to some embodiments of the presentdisclosure. As with the description above, in this process, the locationof the UE 54 is determined by the baseband unit 12. However, in allembodiments, while the description focuses on the baseband unit 12, thepresent disclosure is not limited thereto. The UE location calculator 24may be implemented at some other node in the wireless network (e.g., ata Mobility Management Entity (MME) that communicates with thedistributed antenna wireless system 10).

As illustrated, the RRH 16 that is closest to the UE 54 is determined,e.g., using the process of FIG. 6 (step 200). Then, in order to improvethe precision of the location estimation, a triangulation procedure isperformed. More specifically, the baseband unit 12 assigns andconfigures a receiver 18 of the closest RRH 16 for one receive branch asON and a receiver 18 of each of multiple neighboring RRHs 16 fordifferent receive branches as ON, while assigning and configuring allother receivers 18 of those RRHs 16 as OFF (step 202). For example,looking briefly at FIG. 3A, assume that the closest RRH 16 is RRH 9.Then, for example, the receiver 18-A of RRH 9 is assigned and configuredas ON. Also, the receivers 18-B, 18-C, and 18-D of neighboring RRHs 5,10, and 14 are assigned and configured as ON. All other receivers 18 ofthe RRHs 5, 9, 10, and 14 are assigned and configured as OFF. Notably,step 202 is only an example. More generally, the closest RRH 16 and theneighboring RRHs 16 are assigned different ON/OFF patterns for theirrespective receivers 18, where these different ON/OFF patterns may ormay not activate more than one receiver 18 of the RRHs 16.

The baseband unit 12 then triggers an uplink transmission by the UE 54(step 204). The baseband unit 12, and in particular the UE locationcalculator 24, then triangulates the location of the UE 54 based on theresulting combined signals for the receive branches (step 206). Inparticular, based on the known frequency resource(s) used by the UE 54for the uplink transmission and the known ON/OFF patterns for theclosest RRH 16 and the neighboring RRHs 16 assigned and configured instep 202, the baseband unit 12 can isolate the signals received from theclosest RRH 16 and the neighboring RRHs 16 and triangulate the locationof the UE 54 based on these signals. This isolation can be providedusing the FFT bank 26, but is not limited thereto. Taking into accountthe various cable lengths between the IRU 14 and the RRHs 16, the signalstrength and time of delay delta can be used to calculate how far awaythe UE 54 is from the closest RRH 16 and the neighboring RRHs 16.Triangulation from these data points can then be performed to accuratelydetermine the location of the UE 54.

In some embodiments, the number of RRHs 16 is greater than the number ofON/OFF patterns available to assign to the RRHs 16. For example, in a4×4 MIMO system, there may be, e.g., 16 available codes, but there maybe more than 16 RRHs 16. FIGS. 7A and 7B illustrate a process fordetermining the location of a UE that is particularly well-suited for,but not limited to, this scenario. As illustrated, a number N=N_(TOTAL)RRHs 16 are divided into M zones (step 300). N_(TOTAL) is the totalnumber of RRHs 16 in the geographic area to be searched. This may be,for example, the total number of RRHs 16 connected to the IRU 14 or atotal number of RRHs 16 connected to multiple IRUs 14. M is, in thisexample, a select number of a total number of available unique ON/OFFpatterns. For example, if the total number of available unique ON/OFFpatterns is 16 (e.g., in the 4×4 MIMO case), M may be some select numberof those 16 patterns (e.g., 8 ON/OFF patterns). The M ON/OFF patternsmay include all available (i.e., all possible) ON/OFF patterns (e.g.,all 16 available ON/OFF patterns for 4×4 MIMO) or some subset of allavailable ON/OFF patterns (e.g., some predefined subset of the 16possible ON/OFF patterns for 4×4 MIMO).

The baseband unit 12 assigns and configures a different ON/OFF patternfor each of the M zones (step 302). As such, all of the RRHs 16 in thesame zone are assigned and configured the same ON/OFF pattern. However,RRHs 16 in different zones are assigned with different ON/OFF patterns.The baseband unit 12 triggers an uplink transmission by the UE (step304). The baseband unit 12 analyzes the resulting combined signalsreceived by the different receive branches of the distributed antennawireless system 10 in the manner described above to determine the zonein which the UE is located (step 306). More specifically, the basebandunit 12 analyzes the combined signals for the time and frequencyresources used for the uplink transmission to determine an observedON/OFF pattern in the manner described above. The baseband unit 12 thendetermines which zone was assigned and configured with the observedpattern. That zone is then identified as the zone in which the UE islocated.

If number of RRHs 16 in the identified zone (N_(RRHs) _(_) _(ZONE)) isgreater than a predefined threshold (step 308; YES), then the RRHs 16 inthe identified zone are divided into J subzones (step 310). Thepredefined threshold may be less than or equal to the total number ofavailable ON/OFF patterns. As an example, the predefined threshold maybe M. J is a select number of ON/OFF patterns. More specifically, J canbe less than or equal to the total number of available ON/OFF patterns.Further, in some embodiments, J may be equal to M, but is not limitedthereto.

The baseband unit 12 assigns and configures a different ON/OFF patternfor each of the J subzones (step 312). As such, all of the RRHs 16 inthe same subzone are assigned and configured the same ON/OFF pattern.However, RRHs 16 in different subzones are assigned with differentON/OFF patterns. The baseband unit 12 triggers an uplink transmission bythe UE (step 314). The baseband unit 12 analyzes the resulting combinedsignals received by the different receive branches of the distributedantenna wireless system 10 in the manner described above to determinethe subzone in which the UE is located (step 316). More specifically,the baseband unit 12 analyzes the combined signals for the time andfrequency resources used for the uplink transmission to determine anobserved ON/OFF pattern in the manner described above. The baseband unit12 then determines which subzone was assigned and configured with theobserved pattern. That subzone is then identified as the subzone inwhich the UE is located. The process then returns to step 308 and isrepeated for the identified subzone.

Once the number of RRHs 16 in the identified (sub)zone is less than orequal to the predefined threshold, the process proceeds as describedabove. Specifically, the baseband unit 12 assigns and configures adifferent ON/OFF pattern for each of the RRHs 16 in the identified(sub)zone (step 318). The baseband unit 12 triggers an uplinktransmission by the UE (step 320). The baseband unit 12 analyzes theresulting combined signals received by the different receive branches ofthe distributed antenna wireless system 10 in the manner described aboveto determine the closest RRH 16 to the UE (step 322). More specifically,the baseband unit 12 analyzes the combined signals for the time andfrequency resources used for the uplink transmission to determine anobserved ON/OFF pattern in the manner described above. The baseband unit12 then determines which RRH 16 was assigned and configured with theobserved pattern. That RRH 16 is then identified as the RRH 16 that isclosest to the UE. The location of the UE can then be estimated as beingwithin some predefined range from the known location of the RRH 16. Asdiscussed above, optionally, steps 318-322 may be repeated for a newON/OFF pattern assignment(s), and the UE location can be determinedbased on the results (steps 324 and 326). Also, while not illustrated,once the closest RRH 16 is determined, the process of FIG. 6 may, insome embodiments, be performed to improve the precision of thedetermined location of the UE.

Note that the process of FIGS. 7A and 7B may be further extended tomultiple base stations, or eNBs. In this extension, the process may,e.g., first isolate the base station that a particular wireless deviceof interest is associated with and then, as described above, search forthe closest RRH 16.

The location of the UE determined according to any of the embodimentsdescribed herein can be used for various purposes (e.g., Enhanced-911(E911), location-based services, etc.). FIG. 8 illustrates one exampleof a use of the location of a UE 54. In this example, the location ofthe UE 54 is utilized for interference mitigation and/or beam-forming.This may be particularly beneficial in implementations in which the RRHs16 utilize the same unregulated RF frequency band. As illustrated, inthis example, the RRHs 16 are implemented in RRH enclosures 56-1 through56-N (generally referred to as RRH enclosures 56) along with anadditional set of RRHs 58-1 through 58-N (generally referred to hereinas RRHs 58). These two sets of RRHs 16, 58 are referenced as set α andset β. Each RRH enclosure 56 includes one RRH 16 from set α and one RRH58 from set β.

Upon determining that the UE 54 is closest to, in this example, the RRH16-1 and that only the RRH 16-1 is needed to serve the UE 54, the RRH58-1 can be turned OFF, at least as it pertains to serving the UE 54.Likewise, since the other RRHs 16 and 58 are not needed to serve the UE54, those RRHs 16 and 58 can be turned OFF. However, in this example, atsome distance away from UE 54, another UE 60 is located closest to theRRH 16-N (or the RRH 58-N). In this example, the RRH 58-N is activatedto serve the UE 60, whereas the RRH 16-N is deactivated. In other words,the RRH 16-1 can be used to form a beam toward the UE 54, and the RRH58-N can be used to form a beam toward the UE 60. This reduces thepossibility of collision and mitigates interference. Finer granularitycan be provided by switching individual RF branches within the RRHs 16,58.

Some non-limiting advantages of at least some embodiments of the systemsand methods described herein are as follows.

-   -   Simplicity: In some embodiments, the processes described herein        can be limited to being implemented within a base        station/distributed antenna wireless system 10 and there is no        impact to other network nodes, e.g., the MME and/or no special        application to be installed on the UE.    -   Low Costs: Some embodiments of the present disclosure may use        existing equipment of a distributed antenna wireless system. No        special or new equipment is required. As a result, such        implementations do not require any capital investment (Capital        Expenditures (CAPEX)) of special equipment or continuous        maintenance cost (Operational Expenditures (OPEX)).    -   Fast: Some embodiments of the present disclosure may allow to        determine the location of a UE in an amount of time that is in        the order of seconds.    -   Improved Precision: The resolution of the UE location is down        to, at least, an individual RRH 16. In some implementations,        this provides a precision in the order of 20 m or less.    -   Ease of Use: Some embodiments of the present disclosure do not        require any modification to the deployment and may be enabled        remotely at a central office. There is no need of any field        involvement.

The following acronyms are used throughout this disclosure.

-   -   3GPP Third Generation Partnership Project    -   A/D Analog to Digital    -   CAPEX Capital Expenditures    -   CSRIC Communications Security, Reliability, and Interoperability        Council    -   D/A Digital to Analog    -   E911 Enhanced-911    -   eNB Enhanced or Evolved Node B    -   FCC Federal Communications Commission    -   FFT Fast Fourier Transform    -   GPS Global Positioning System    -   I/O Input/Output    -   IRU Intermediate Radio Unit    -   LTE Long Term Evolution    -   m Meter    -   MIMO Multiple Input Multiple Output    -   MME Mobility Management Entity    -   OPEX Operational Expenditures    -   RF Radio Frequency    -   RRH Remote Radio Head    -   RX Receiver    -   UE User Equipment

Those skilled in the art will recognize improvements and modificationsto the embodiments of the present disclosure. All such improvements andmodifications are considered within the scope of the concepts disclosedherein and the claims that follow.

What is claimed is:
 1. A method of operation of a node associated with adistributed antenna wireless system to determine a geographic locationof a wireless device, comprising: obtaining one or more combined receivesignals responsive to a transmission by the wireless device, wherein:the distributed antenna wireless system comprises a plurality of remoteradio heads each comprising one or more receivers; and the one or morecombined receive signals comprises, for each receive branch of one ormore receive branches of the distributed antenna wireless system, acombined receive signal that is a combination of signals received by thereceivers comprised in the receive branch in accordance with differentsimultaneous ON/OFF patterns assigned to the plurality of remote radioheads for the one or more receive branches; and analyzing the one ormore combined receive signals to determine information indicative of thegeographic location of the wireless device.
 2. The method of claim 1wherein: each remote radio head of the plurality of remote radio headscomprises a plurality of receivers; the one or more receive branches isa plurality of receive branches wherein each receive branch of theplurality of receive branches comprises a combination of one receiver ofthe plurality of receivers from each of the plurality of remote radioheads; and the one or more combined receive signals is a plurality ofcombined receive signals that comprise, for each receive branch of theplurality of receive branches, the combined receive signal that is thecombination of signals received by the receivers comprised in thereceive branch in accordance with different simultaneous ON/OFF patternsassigned to the plurality of remote radio heads for the plurality ofreceive branches.
 3. The method of claim 2 further comprising assigningthe different simultaneous ON/OFF patterns to the plurality of remoteradio heads for the plurality of receive branches.
 4. The method ofclaim 3 wherein assigning the different simultaneous ON/OFF patterns tothe plurality of remote radio heads for the plurality of receivebranches comprises randomly assigning the different simultaneous ON/OFFpatterns to the plurality of remote radio heads for the plurality ofreceive branches.
 5. The method of claim 2 further comprisingconfiguring the plurality of remote radio heads with the differentsimultaneous ON/OFF patterns assigned to the plurality of remote radioheads for the plurality of receive branches.
 6. The method of claim 2wherein the signals received by the receivers are combined by anIntermediate Radio Unit, IRU, and the method further comprisesconfiguring the IRU with the different simultaneous ON/OFF patternsassigned to the plurality of remote radio heads for the plurality ofreceive branches.
 7. The method of claim 2 wherein analyzing theplurality of combined receive signals comprises: obtaining measurementsof received signal energy and/or one or more signal characteristics forthe plurality of combined receive signals within a predefined frequencyrange used for the transmission by the wireless device during acorresponding time window; and comparing the measurements for theplurality of combined receive signals to the different simultaneousON/OFF patterns assigned to the plurality of remote radio heads for theplurality of receive branches of the distributed antenna wireless systemto identify one of the plurality of remote radio heads that is closestto the wireless device as a closest remote radio head.
 8. The method ofclaim 7 further comprising: changing the different simultaneous ON/OFFpatterns assigned to the plurality of remote radio heads; and afterchanging the different simultaneous ON/OFF patterns assigned to theplurality of remote radio heads, repeating the process of obtaining theplurality of combined receive signals responsive to the transmission bythe wireless device and analyzing the plurality of combined receivesignals to determine the information indicative of the geographiclocation of the wireless device.
 9. The method of claim 7 furthercomprising: assigning and configuring a different ON/OFF pattern for theclosest remote radio head and each remote radio head of multipleneighboring remote radio heads of the closest remote radio head;triggering a second transmission by the wireless device; andtriangulating the geographic location of the wireless device based onsecond combined signals obtained for the plurality of receive branchesof the distributed antenna wireless system responsive to the secondtransmission by the wireless device.
 10. The method of claim 2 furthercomprising using the information indicative of the geographic locationof the wireless device to selectively activate transmitters and/orreceivers of one or more of the plurality of remote radio heads forcommunication with the wireless device.
 11. A node associated with adistributed antenna wireless system operable to determine a geographiclocation of a wireless device, comprising: a subsystem operable to:obtain one or more combined receive signals responsive to a transmissionby the wireless device, wherein: the distributed antenna wireless systemcomprises a plurality of remote radio heads each comprising one or morereceivers; and the one or more combined receive signals comprises, foreach receive branch of one or more receive branches of the distributedantenna wireless system, a combined receive signal that is a combinationof signals received by the receivers comprised in the receive branch inaccordance with different simultaneous ON/OFF patterns assigned to theplurality of remote radio heads for the one or more receive branches;and analyze the one or more combined receive signals to determineinformation indicative of the geographic location of the wirelessdevice.
 12. The node of claim 11 wherein: each remote radio head of theplurality of remote radio heads comprises a plurality of receivers; theone or more receive branches is a plurality of receive branches whereineach receive branch of the plurality of receive branches comprises acombination of one receiver of the plurality of receivers from each ofthe plurality of remote radio heads; and the one or more combinedreceive signals is a plurality of combined receive signals thatcomprise, for each receive branch of the plurality of receive branches,the combined receive signal that is the combination of signals receivedby the receivers comprised in the receive branch in accordance withdifferent simultaneous ON/OFF patterns assigned to the plurality ofremote radio heads for the plurality of receive branches.
 13. The nodeof claim 12 further comprising an ON/OFF pattern assignment generatoroperable to: assign the different simultaneous ON/OFF patterns to theplurality of remote radio heads for the plurality of receive branches;and configure the plurality of remote radio heads with the differentsimultaneous ON/OFF patterns assigned to the plurality of remote radioheads for the plurality of receive branches.
 14. The node of claim 12wherein the signals received by the receivers are combined by anIntermediate Radio Unit, IRU, and the node further comprises: an ON/OFFpattern assignment generator operable to: assign the differentsimultaneous ON/OFF patterns to the plurality of remote radio heads forthe plurality of receive branches; and configure the IRU with thedifferent simultaneous ON/OFF patterns assigned to the plurality ofremote radio heads for the plurality of receive branches.
 15. The nodeof claim 12 wherein the subsystem comprises: circuitry operable toobtain measurements of received signal energy and/or one or morecharacteristics for the plurality of combined receive signals within apredefined frequency range used for the transmission by the wirelessdevice during a corresponding time window; and a location calculatoroperable to compare the measurements for the plurality of combinedreceive signals to the different simultaneous ON/OFF patterns assignedto the plurality of remote radio heads for the plurality of receivebranches of the distributed antenna wireless system to identify one ofthe plurality of remote radio heads that is closest to the wirelessdevice as a closest remote radio head.
 16. The node of claim 15 whereinthe subsystem is further operable to: change the different simultaneousON/OFF patterns assigned to the plurality of remote radio heads; andafter changing the different simultaneous ON/OFF patterns assigned tothe plurality of remote radio heads, repeat the process of obtaining theplurality of combined receive signals responsive to the transmission bythe wireless device and analyzing the plurality of combined receivesignals to determine the information indicative of the geographiclocation of the wireless device.
 17. The node of claim 15 wherein thesubsystem is further operable to: assign and configure a differentON/OFF pattern for the closest remote radio head and each remote radiohead of multiple neighboring remote radio heads of the closest remoteradio head; trigger a second transmission by the wireless device; andtriangulate the geographic location of the wireless device based onsecond combined signals obtained for the plurality of receive branchesof the distributed antenna wireless system responsive to the secondtransmission by the wireless device.
 18. The node of claim 12 whereinthe node is further operable to use the information indicative of thegeographic location of the wireless device to selectively activatetransmitters and/or receivers of one or more of the plurality of remoteradio heads for transmission to the wireless device.
 19. A distributedantenna wireless system, comprising: a plurality of remote radio headseach comprising one or more receivers; an Intermediate Radio Unit, IRU,operable to combine, for each receive branch of one or more receivebranches of the distributed antenna wireless system, signals received bythe receivers comprised in the receive branch to provide a combinedreceive signal for the receive branch; and a baseband unit operable to:assign and configure different simultaneous ON/OFF patterns for theplurality of remote radio heads for the one or more receive branches;trigger a transmission by a wireless device; obtain one or more combinedreceive signals responsive to the transmission by the wireless device,where the one or more combined receive signals are in accordance withthe different simultaneous ON/OFF patterns assigned and configured forthe plurality of remote radio heads for the one or more receivebranches; and analyze the one or more combined receive signals todetermine information indicative of a geographic location of thewireless device.
 20. The distributed antenna wireless system of claim 19wherein: each remote radio head of the plurality of remote radio headscomprises a plurality of receivers; the one or more receive branches isa plurality of receive branches wherein each receive branch of theplurality of receive branches comprises a combination of one receiver ofthe plurality of receivers from each of the plurality of remote radioheads; and the one or more combined receive signals is a plurality ofcombined receive signals that comprise, for each receive branch of theplurality of receive branches, the combined receive signal that is acombination of signals received by the receivers comprised in thereceive branch in accordance with the different simultaneous ON/OFFpatterns assigned to the plurality of remote radio heads for theplurality of receive branches.